Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $23.85   9.188%   $26.0413   $26.04   $26.05   $26.00  
  Purchase #2 $172.62   13.520%   $195.9582   $195.96   $195.95   $196.00  
  Purchase #3 $143.31   9.432%   $156.827   $156.83   $156.85   $156.80  
  Purchase #4 $58.32   9.717%   $63.987   $63.99   $64.00   $64.00  
  Purchase #5 $164.39   8.314%   $178.0574   $178.06   $178.05   $178.10  
  Purchase #6 $182.47   3.595%   $189.0298   $189.03   $189.05   $189.00  
  Purchase #7 $161.31   13.465%   $183.0304   $183.03   $183.05   $183.00  
  7 purchase totals = $906.27       $992.9311   $992.94   $993.00   $992.90